Isn't damp odd?

[Zebra]

I mean, really unpredictable in the way it behaves. A week ago I lime plastered the external back wall of the house, and hung tarpaulins over it to keep it from drying out too fast. Now all of a sudden the inside of the fireplace is soggy as a soggy thing, a film of moisture over it, wetter than it's ever been, and the only reason I can think of is that the water can't evaporate from the back wall over a metre away. Really odd.

 

[Flyfisher]

Are you sure it's not condensation? The recent spell of warm weather has caused some condensation in our house as humid air has wafted through and met some thick walls that are still at last week's lower temperature.

 

[LadyArowana]

Yes, damp is odd, but not just in houses. Why do wafer biscuits go soggy and not very nice if the packet is left open, but a slice of bread dries out ( and becomes equally unpalatable ) ? I'm sure there is a deeply scientific reason involving relative humidity levels and the natural moisture content of the foodstuff, but I just find it strange and annoying.

 

[middi]

There is nothing ODD about damp.

It is water vapour that is " sucked " into a permeable substrate ( usually warmer ) , by conduction or convection.

The rate and direction of movement and eventual evaporation is determined by the air temperature and air flow moving across the saturated substrate. As air flow travels across the saturated substrate, it will remove the surface moisture, this moisture is then replaced by more moisture that is still trapped within the substrate and the cycle continues. The faster the air flow and temperature, the quicker the moisture is removed or " sucked" back out. ( and then it rains again or someone decides to point the hose pipe towards the substrate or wet RENDER the substrate).

Moisture that gains entry within a permeable and breatheable substrate will carry on perculating through the substrate where, eventually, it will be dissipated back to the atmosphere, or " sucked " out by a dry air flow.

In your case, rendering the outside wall, a lot of the moisture would have travelled ( or sucked) into the dry wall section where a certain amount of moisture would have be dissipated within the building, depending on air flow and temperature within the building it would determine the speed of evaporation. Also, the fact that the external wall had to be covered to stop the cracking process, and dependant on the permeability of the covering, a restriction of air flow across the external wall surface was induced forcing more moisture to evaporate within the building.

Assuming that it would have been possible to leave the external rendered walls exposed to blazing sunshine in windy conditions, you would have had hardly any " hint" of moisture within the building, it would have evaporated outwards faster than it would have travelled inwards.

Damp, it is a question of balance between the amount of water vapour to be removed in relation to the amount of air flow to remove it.

Middi

 

[LadyArowana]

There is nothing ODD about damp.

It is water vapour that is " sucked " into a permeable substrate ( usually warmer ) , by conduction or convection.

The rate and direction of movement and eventual evaporation ...............................
Middi

I bet you never have soggy wafers or stale bread either :lol:

 

[middi]

I just preach, I don't do, Lady A ( It is really satisfying sitting on the fence :wink: ). The amount of french sticks and digestive bisquits I have ( or my wife has) thown away is embarassing

 

[LadyArowana]

I just preach, I don't do, Lady A ( It is really satisfying sitting on the fence :wink: ). The amount of french sticks and digestive bisquits I have ( or my wife has) thown away is embarassing

I wonder if the chocolate coating on a kit kat acts like render on a building and stops the moisture movement keeping the wafer nice? I think Mr P should do some research. Assuming he doesn't eat them all the moment the wrapper is off :lol:

 

[middi]

Does your imagination have no bounds Lady A ?. If Mr P joins the " moisture" party God knows what this thread will turn into :lol:

Middi

 

[Zebra]

Hmm, Flyfisher that sounds very plausible, perhaps that's what it is. Lady A, I can't work out whether you're saying I should have rendered the walls in chocolate, or whether that would have been a decidedly bad idea.

 

[Sandsni]

Mmm chocolate-rendered walls, now there's a thought :wink: .

Middi, I wish I'd had you on hand when I was trying to explain relative humidity to a letting agent who insisted that a wall should be able to dry out naturally during the wettest April on record without any heat or ventilation... :?

 

[LadyArowana]

Hmm, Flyfisher that sounds very plausible, perhaps that's what it is. Lady A, I can't work out whether you're saying I should have rendered the walls in chocolate, or whether that would have been a decidedly bad idea.

How about starting with a small test project first and see how that goes before moving on to the full Hansel and Gretel gingerbread effect over the entire house?

 

[Penners]

If Mr P joins the " moisture" party God knows what this thread will turn into

Ahem - it will turn into the cerebral, intellectual debate that is the destiny of so many PPUK threads, signore. :wink:

Milady - the one factor that hasn't yet been fully aired (geddit - aired? :lol in this discussion is the inherent moisture content of the item under discussion.

In the case of your example, the wafer biscuits have a very low moisture content, and are presumably rather hygroscopic. Hence they absorb moisture from the atmosphere (which has a higher relative humidity) readily and quickly. The bread, however, is very moist in its fresh state - much more so than the ambient air. Hence it gives off its moisture to the air when allowed to do so. So the wafers are trying to turn into bread, and the bread into wafers - whereas in fact they both end up roughly halfway between the two.

See? Cogent, well-argued (and complete guesswork).

 

[Zebra]

I can't work out whether you're saying I should have rendered the walls in chocolate, or whether that would have been a decidedly bad idea.

Just went onto SPAB's website to find out the answer to that question, and found this, which some of you may be interested in:

"Popular in the 1970s as a building material, the Kit-Kat has been enjoying a resurgence in recent years as architects and specifiers realise the advantages of the durability of its chocolate layer combined with the insulation value of its wafer layer. One must remember when selecting Kit-Kats for construction purposes however, never to be tempted to use Kit-Kats which have been dunked, as interstitial tea will lead to rapid deterioration of any chocolate based structure."

 

[Feltwell]

Just a shame that Kit Kats are made by Nestle, who have not enjoyed the best of reputations for their ethics over the years - particularly with regards to how they sell baby milk in developing countries.

 

[Penners]

never to be tempted to use Kit-Kats which have been dunked

What a preposterous notion! Dunk a Kit-Kat...?! :shock:

 

[Sandsni]

never to be tempted to use Kit-Kats which have been dunked

What a preposterous notion! Dunk a Kit-Kat...?! :shock:

You've obviously never tried a white Kit-Kat dunked in coffee I wouldn't waste it on a wall though :shock:

 

[LadyArowana]

You've obviously never tried a white Kit-Kat dunked in coffee I wouldn't waste it on a wall though :shock:

For traditional period property assessment time only the original kit kat and tea is appropriate. :lol: :lol: :lol:

 

[AMc]

Just a shame that Kit Kats are made by Nestle, who have not enjoyed the best of reputations for their ethics over the years - particularly with regards to how they sell baby milk in developing countries.

Indeed, I haven't bought anything from them for as long as I remember and sadly this has deprived me of many of my old Rountree favourites since 1988 when they were acquired. I'm sure that they don't care at all but I can't bear to give them my money.

 

[Penners]

To my shame, I find that the Kit-Kat addiction transcends the pricks of conscience.

 

[Sandsni]

I honestly thought Nestle had given up the baby-food-to-developing-countries idea after the outcry back then. Now I have to rethink my dunking (I normally try to buy fair trade chocolate but occasionally the Kit Kat was too tempting )